Radio position finding



ec, 23,17. D, 3, Q LUCK 2,433,283

` RADIO POSITION FINDING Filed Nov. 2, 1942 2 Sheets-Sheet '1 ,1, @Aw-raam' n Hevia/waa'. m7@ qf/vfra 056. Ff@

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attorney Dec. 23, 1947. D. G. c. LUCK RADIO POSITION :FINDING Filed Nov. 2, 1942 2 Sheets-Sheet 2 Nkkm nvenfor cH Gttorneg Patented Dec. 23, 1947 RADIO POSITION FINDING David G.

Radio of Delaware C. Luck, Hightstown, N. J., assignor to Corporation of. America, a corporation Application November 2, 1942, Serial No. 464,178 Claims. (Cl. Z50-1.68)

This invention relates to radio position nding, and more particularly to determining the' position of a mobile craft with respect to a plurality of xed stations by observing the propaga.- tion times required for radio waves to travel between said craft and said stations.

It is an object of this invention to provide an method of and means for deriving an of the distance between two stations.

object is to provide an improved and means for utilizing a plurality of such indications to automatically plot the map position Iof a mobile station with respect to two or more fixed stations. Y

These and other. objects will become apparent to those skilled in the art upon consideration of the following description, with refer-ence to the accompanying drawings, of which Fig. 1 is a schematic block diagram of a distance indicating system, according to the invention, Fig. 2 is av block diagram of the echo station of Fig. 1, and Fig. 3 is a schematic block diagram of a complete system for providing automatically an indication a mobile station with reference to two fixed stations. Similar reference characters designate similar elements in the drawings.

Referring to Fig. 1, the mobile station includes an oscillator I coupled through an amplifier 3 to an antenna 5, and through a modulator 'I to a second antenna 9. The oscillator I is frequency modulated by the output of a sawtooth Wave generator Il. A second oscillator I3 is connected to the modulator 1. An antenna I5 is connected to a receiver I1. 'I'he output circuit of the receiver I'I is connected toa frequency responsive indicator, such as an averaging cycle counter I9 and a meter 2|. station is indicated by the block 6.

The fixed station (Fig. 2) includes a receiver 25 and a transmitter 23. 'I'he output circuit of the receiver 25 is connected through a modulator 21 to the transmitter 23. A local oscillator 29 is connected to the modulator 21.

The operation of the system is as follows: The receiver 25 and the amplifier 3 are tuned to one carrier frequency, f, and the receiver Il and the transmitter 23 are tuned to another carrier frequency, (F-I-F). The oscillators I3 and 29 are both adjusted to operate at the frequency F. The frequency of the oscillator I is cyclically varied about the carrier frequency j as a mean, by-the sawtooth output of the generator II, starting each cycle at its minimum value fo and increasing linearly at a rate df/dt which depends An echo or fixed' on the slope Iof the sawtooth Wave. This variable fr equency signal is amplified by the amplifier 3 and transmitted from the antenna 5 at the velocity of light, c. Thus if the lfrequency transmitted at the instant t is fo, the frequency of the signal reaching the echo station 6 will be fo at a later time t'. The interval t'-t is the propagation time of the signals from the mobile station to the echo station.

The signal received at the echo station is converted in the modulator 21 to the carrier frequency f-I-F, and retransmitted, after a short delay period, T, by the transmitter 23. The retransmitted signal carries the same frequency variations as the original signal; it is merely shifted in frequency by the amount F. The sier nal fn-I-F is thus retransmitted at the time t'}-T. The time required for this signal to return to the mobile station is again the interval t-t, assuming that the movement of the mobile station is negligible in the time 2(t-t). The total time from the transmission of the frequency fo to the return of the frequency ,fc4-F is thus 2(t-t) -l-T. Since the signals travel at the Velocity of light, c, tl'ie time tt is the distance, d, between the two stations, divided by c. The total time is ceived at the antenna l5 from the echo station 6, the frequency of the oscillator I is This signal is converted by the modulator 'l and oscillator I3 to a frequency foi-gewalt +13' and transmitted over a negligible (negligible because both devices are located on the mobile station) distance to the antenna I5. The in put to the receiver I1 thus comprises two voltages, differing in frequency by the amount providing a. beat note of this frequency in the output of the receiver. Since the quantities The indication of the meter 2| is thus related linearly to the distance d. The frequency fo may be, for example, 300 megacycles per second,df/dt 30 megacycles per second per second, the sawtooth frequency 100 cycles per second, and the retransmission delay T a few microseconds, so that T may be neglected for all but very short distances. These values are suitable for the measurements of distances up to which the direct transmission path becomes blocked by the curved surface of the earth.

A value of d given by a system such as that of Fig. 1 establishes the position of the mobile craft as on a circle of radius d about the fixed echo station. By using two suitably located echo stations, each retransmitting on a separate channel, and a receiver and frequency meter atthe mobile station for each channel, the position of the mobile station can be established as at an intersection of the two circles ing to the two iixed station locations and the two corresponding values of d. To give a check, and also to determine which of the two intersections is relevant, a third fixed station and a third channel may be used. The circles may be plotted on a map or chart to determine the position of the mobile station.

The plotting may be done automatically by use of a multiple gun cathode ray tube arranged as shown in Fig. 3; The mobile station includes an oscillator l, amplifier 3, antennas 5', 9 and l5, modulator 1, oscillator I3, receiver i1, and counter I9, connected like the correspondingly designated parts of the system of Fig. 1. A second channel, including a modulator lator H3, receiver ||1, and counter |19, is arranged in the same manner as the first channel, but is operated at a diiferent conversion frequency F. The counters i9 and ||9 may be of the. type described in Schwartz, U. S. lratentl 2,137,859. The outputs of the cycle counters I9. and llt are direct voltages proportional respectively to the distances d and d' of thev echo stations 6 and H16 from the` mobile station.

A double gun cathode raytube 3| is connected to a power supply 33. One set of deflection circuits 34, 35`is connected to'an adjustable centering control circuit 31. The other deflection circuits 39 and 4| are similarly connected to a centering control circuit 43.

An oscillator i5 is connected through modulators 41 and 49 to phase splitting circuits 5| and 53 respectively` The two-phasek outputs of the circuits 5| and 53 are'superirnposed on the centering voltages provided by the circuits d3 and 31 to the lrespective deection circuits.

The phase splitting and centering circuits associated with each deilection system of the cathode ray-'tube 3| -may vbe identicalA withthose shnwn on Page 365 of RCA Review, vol. VI, No. 3, J anucorrespondlill, oscilf 4 ary, 1942, in the section marked cathode ray indicator of the drawing, Figure 17.

In operation, the two-phase voltages derived from the output of the oscillator by the phase splitters 5| and 53 are applied to the respective deection circuits to provide circular traces and 51 of the electron beams upon the screen of the tube 3|. These traces are centered about points 59 `and 6| respectively, which are adjusted by means of the centering controls 31 and 43 to positions corresponding to the map positions of the echo stations E and |06. The radii of the traces 55 and 51 depend on the quantities of the output of the oscillator 45 which are applied to the respective deiiection circuits. These are controlled by the modulators 41 and 49 in response to the D.C. outputs of the respective counters |9 and I9. Thus the position of the mobile station is indicated at one of the points of intersection 63 and 65 of the two traces.

Thus the invention has been described as an improved radio position finding system.Y Frequency modulated signals are radiated from a mobile station, picked up, changed in frequency and retransmitted by a xed station. The frequency of the retransmitted wave is compared at the mobile station with that of the wave being transmitted from the fixed station. The difference is related to the time of travel of the signals between the two stations, and provides a direct measure of the distance. Two or more such systems are. used to determine the position of the mobile station with respect to the fixed stations. The position may be plotted automatically on a cathode ray tube by tracing circles, of radii proportional to the respective distances, centered about points corresponding to the map positions of the xed stations.

I claim as my invention:

1. A radio distance measuring system comprising a control station and an echo station, means at said control station for radiating two similarly frequency modulated signals differing in frequency by a predetermined amount, a receiver atk said echo station tuned to respond to one of said signals, a frequency changer connected to' said receiver and adjusted to chan-ge the frequency of the output thereof by said predetermined amount, a transmitter connected tok said -frequency changer to radiate said frequency changed signal, a receiver at saidl controlY station tuned to respond to saidreradiated signall and to the other of said radiated signals, andbeat frequency responsive means connected to said receiver-to respond to thedifference'v in frequency of said lattertwo signals.

2. A radio distance measuring system comprising a control station and an echo station, means at said controlv station for radiating afrequencyV modulated signal and' forA generating' s, second signal diieringfrom said; radiatedv signal by a predetermined frequency, means at said echo station tuned to receivefsaidf radiated-'signal and to radiate a similarly modulated signal quency differing` from said received signal! by said predetermined frequency, means at'said con-trol station tuned to receive-'the signal transmitted from said' echoI station, and means responsive 'tothe difference in frequency signal and said second signal'.

3'. A radio positron indicating. system" comprising a control station, and' a, plurality offspaced' echo stations, means for radiating-a frequencymcdulated signal from said'l control Ystati'onmeans at each of" said .echo stations: for receivingY said-v at frebetween saidf latterfsignal, changing the frequency thereof by a predetermined amount, and retransmitting said changed signals, receivers at said control station tuned to respond to the signals radiated by the respective echo stations, means for comparing the output of each of said receivers with the signal radiated from said control station to derive control voltages proportional to the respective distances of the echo stations from the control stations; a cathode ray tube, deection circuits including an oscillator and phase splitting circuits connected to produce circular sweeps of the beam of said cathode ray tube, and variable gain arnpliiiers connected in said deection circuits and connected to said comparing means to be varied in gain by said control voltages.

4. A radio position determining system comprising a control station and a plurality of spaced echo stations, means for radiating a frequency modulated signal from said control station, means at each of said echo stations for receiving said signal, changing the frequency thereof by a predetermined amount, and retransmitting said changed signals, a cathode ray tube at said control station, deection circuits for said tube including an oscillator and phase splitting circuits connected to produce a plurality of circular scanning patterns on the face of said tube, amplitude control means connected in each of said deiiection circuits, and means responsive to said retransmitted signals and to said initial signal to control said amplitude control means.

5. The method of indicating in the form of intersecting circular traces the position of a mobile station with respect to the positions of a plurality of spaced fixed stations on the luminescent screen a cathode ray tube of the oscilloscope type having conventional deflection means, including the steps of radiating a frequency modulated signal from said mobile station, receiving said signal at each of said xed stations, reradiating said frequency changed signals respectively from each of said xed stations, receiving said reradiated signals at said mobile station, comparing the frequency of each of said received reradiated signals with that of said initial signal to derive control voltages proportional to the frequency differences, producing circular traces on said screen of said cathode ray tube, andgcontrolling the respective radii of said traces in accordance with said control voltages.

D. G. C. LUCK.

REFERENCES CITED The following referenceslare of record in the le of this patent:

UNITED STATES PATENTS 

